The field of radiation therapy (also known as “radiotherapy”), along with the sub-field of radiation oncology, seeks the control or treatment of biological processes through the use of electromagnetic radiation. Radiation therapy has been in use in some form for over a century, shortly following the discovery of X-Rays by Wilhelm Röntgen, in November of 1895. Generally speaking, radiation therapy accomplishes its goals by targeting living tissues with ionizing radiation, altering the tissue's size, structure, composition and function. For example, in cancer therapy, a beam of ionizing radiation may be focused spatially on a malignant tumor, destroying, among other things, the malfunctioning DNA which has caused it to de-differentiate from healthy to malignant tissue, and, thereby, arresting the disease process. Radiation therapy is especially useful in treating “inoperable” tumors, where the size and location create unacceptable dangers or where the prognosis for recurrence despite surgery is especially great, and surgical solutions are either deemed to be ineffective options, or to present too great a risk of injury or earlier death when weighed against the potential successful removal of the tumor.
Within the sub-field of radiation oncology, linear accelerator machines (“LINACs”) that generate megavoltage X-rays for deep-tissue penetration are currently in heavy use. LINACs are a form of “external beam” radiation therapy, in the sense that they generate radiation from outside of the treatment area and patient's body, and focus it inward toward the tumor. Other forms of radiation therapy include brachytherapy and systemic radioisotopes (where the radiation source is inserted, or taken by pill or injection, respectively). Like surgical intervention, brachytherapy causes collateral damage to healthy tissue from the trauma of the procedure. Systemic radioisotopes are even more rarely used, due to difficulties in targeting tumors or other targets, and system-wide collateral damage.
Although LINACs have the advantage of avoiding some of the tissue damage and other risks of invasive surgery and brachytherapy, and can cause less damage than systemic radioisotopes, they also present their own drawbacks. In most instances, the external beam of radiation must first pass through healthy, surrounding tissues before reaching the tumor. As a result, those tissues are also damaged, by the same process that damages the tumor tissue. And because a radiation beam can ionize the DNA of any biological cell in its path, LINACs cause mutations in healthy surrounding tissue, which mutations can lead, among other things, to cancer. Thus, ironically, radiation therapy bears a probability of causing new cancer, in addition to otherwise damaging surrounding tissues, even if it succeeds at destroying a current tumor. In addition to causing more cancer, a variety of other radiation therapy side effects are seen in collaterally-damaged, otherwise healthy adjacent tissues, including edema, neural and cognitive decline, hair loss, irritation and heart disease.
In tomotherapy and multiple-source fixed LINAC machines, the radiation source may be applied at a variety of isocentric angles from outside of the treatment area—all of which target the tumor—in order to disperse less of the radiation across a greater volume of healthy tissue, such that it can withstand the impact of the radiation more easily. Beginning in the 1990s, image-guided and intensity-, spatial approach- and beam shape-modulated radiation therapy techniques have been developed, which further seek to target tumors with greater accuracy. These techniques (hereafter, called “IMRT”) use advanced imaging technology and computer-aided dosage plans in conjunction with LINACs and other ionizing radiation sources, to target the diseased tissues and avoid collateral damage to more important healthy tissue with greater accuracy. For example, the RapidArc® machine, from Varian Medical Systems, Inc., employs computer modeling of 360-degree dosage plans (1) modulating the shape of the beam source through its escape aperture (via multiple collimating “leaves” that are extended or withdraw over the aperture) (2) controlling gantry (beam-emitting source) rotation speed, as well as (3) beam intensity, to deliver a more favorable dosage pattern.
Radiation therapy is often carried out over several sessions in a process called “fractionation,” rather than all at once, to give healthy, non-malignant cells more of an opportunity to heal following exposure. However, the diseased tumor cells may have more of a potential to survive treatment as well, through such timing techniques. In addition, the added time needed for radiation therapy treatments is disruptive to the patients' life, as well as expensive and labor-intensive for both the patient and medical staff.
IMRTs employ a variety of particle and electromagnetic wave radiation beams. Most forms of radiotherapy have a decaying ionization profile, meaning that the particle or electromagnetic radiation beam's ionization energy tends to decrease as the beam penetrates deeper into tissue. An exception may be some forms of proton or heavier ion therapy, which exhibit what is known as a “Bragg Curve,” a phenomenon where ionization beam energy peaks shortly before the particles come to rest (assuming they do not fully exit the target or collateral tissue into space). Proton therapy has been rapidly developing in the hope that these heavier ionization decay profiles will allow for greater localization of radiation dosage to tumors, while decreasing dosage to healthy tissues. However, collateral damage is a major issue in these therapies due to significant dosage to healthy collateral tissues.
It is an objective of the present invention to increase the dosage effectiveness of external radiation therapy to target tissues, while decreasing the damage to collateral tissues.
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